1967 Johnson 6hp CD-24S Spark Plugs

[BillyB11]

Hello,

I am new to engine work but I decided to restore a 6hp Johnson '67 that has been sitting in my Grandpa's shed for some years. I am about to order new plugs but have a quick question. Currently, the outboard has Champion J8C plugs in it. According to another website, I should be using Champion J4C plugs. According to the Seloc manual I bought, I need Champion J6J plugs. I have a suspicion the J8C's that are currently on it are not correct (too hot from what I have read), but I am not sure how to reconcile the J6J vs J4C recommendations. Furthermore, in the manual (Seloc) that I bought, it says "Most spark plugs to not come gapped to the proper specification". Is this true, if so, what tools/gauges must I have to gap them myself?

Thanks!
Billy

 

[F_R]

According to the parts book or your motor, you are supposed to use Champion J4J or Auto Lite A21X or AC M42K. The J4J is no longer made, and J4C is the accepted new number. Since J4C are a little bit hard to find, a lot of people say J6C is OK. J8C is stretching it a bit.

 

[racerone]

With a working thermostat the plug to use is a J4C.-----Have you inspected the coils ?---Tested to see if spark will jump a gap of 5/16"

 

[BillyB11]

racerone, what confuses me about your response is this: I assumed (maybe wrongly) that there is a certain spec. plug I need regardless of the thermostat, coils, or other stuff. I would have guessed, that this motor has a plug that is correct, and if there is a problem with something like the thermostat or coils I just need to fix/replace those independently. If I am interpreting your response correctly, it would lead me to believe that the working order of the coils and/or thermostat have some bearing on which plug I need.

Thanks for the responses

 

[racerone]

With the magneto in good condition ( 5/16" spark ) and a working thermostat the motor will troll / idle all day long with J4C.------And I have about 10 of these engines with 2 of them getting rebuilt this winter without the use of a manual.----My knowledge of these fine motors goes way beyond what sparkplugs might be needed to make it start !

 

[BillyB11]

Great, thanks for response racerone, I am grateful that their is someone out there with as much experience/knowledge as you that is willing to respond to these post. I want to use this motor to run my jon boat, but I also want to get some mechanical experience under my belt to make sure I can keep my man card. Hopefully you don't get sick of my stupid questions!

Billy

 

[F_R]

I agree racer knows his stuff. But if I may add 2c, the heat range of a spark plug determines how fast it is able to transfer the heat of combustion from the plug tip to the cylinder head and ultimately to the cooling system. So, in determining a suitable spark plug, the engineers considered the temperature of the cylinder head, which of course is related to a properly operating thermostat. In other words, it's all related. And you are correct, if the thermostat is not working, replace it. That is a separate issue, but related to other matters.

 

[BillyB11]

Great thanks for your input F_R... as to my other inquiry, do I need to gap the plugs when I get them?

 

[boobie]

Yes. Set to .030 ".

 

[BillyB11]

Great, thanks for help everyone!

 

[Vic.S]

Hello,

I am new to engine work but I decided to restore a 6hp Johnson '67 that has been sitting in my Grandpa's shed for some years. I am about to order new plugs but have a quick question. Currently, the outboard has Champion J8C plugs in it. According to another website, I should be using Champion J4C plugs. According to the Seloc manual I bought, I need Champion J6J plugs. I have a suspicion the J8C's that are currently on it are not correct (too hot from what I have read), but I am not sure how to reconcile the J6J vs J4C recommendations. Furthermore, in the manual (Seloc) that I bought, it says "Most spark plugs to not come gapped to the proper specification". Is this true, if so, what tools/gauges must I have to gap them myself?

Thanks!
Billy

,
J indicates a plug with a 14mm thread size and 3/8" reach

4, 6,or 8 indicates the heat range. The higher the number the hotter the plug will run.

J ( after the heat range number) indicates a cut back ground electrode.. C indicates a "copper plus" design.. These replace the "J" type which are obsolete

I believe the currently recommended plugs are J6C, gapped at 0.030" but if it will troll all day with J4Cs, as Racerone says it should, they will be fine

Yes you will have to gap the plugs correctly by bending the ground electrode closer to or away from the centre electrode You will need a feeler gauge or a spark plug gapping tool to do this.

If you happen to live in a part of the globe where NGK plugs are more readily available than Champions B7S will be suitable.